Central nervous system (CNS) infections, such as viral encephalitis, are common causes of morbidity and mortality worldwide. Many neurotropic viruses cause disease by disseminating through the bloodstream to sites of secondary replication within the CNS. However, the mechanisms used by viruses to traverse the endothelium to gain access to the circulation are largely unknown. Reoviruses use hematogenous routes to gain access to the murine CNS, where they cause nonlethal hydrocephalus or lethal encephalitis, depending on the viral serotype. Thus, reoviruses are highly tractable experimental models to study viral hematogenous dissemination to the brain. Junctional adhesion molecule A (JAM-A), a tight junction protein that serves as a receptor for reovirus, is required for the establishment of viremia during reovirus infection of mice. Infection of primary endothelial cells by reovirus is dependent on expression of JAM-A. The central hypothesis of this proposal is that expression of JAM-A on endothelial cells facilitates hematogenous dissemination of reovirus. Three specific aims are proposed to test this hypothesis. In Specific Aim 1, mechanisms by which endothelial JAM-A mediates reovirus infection in vivo will be defined. In Specific Aim 2, the function of endothelial JAM-A in reovirus infection of polarized endothelial cells will be determined. In Specific Aim 3, the role of JAM-A in reovirus egress from the blood brain barrier into the brain will be elucidated. These studies will shed light on basic mechanisms used by viruses to disseminate hematogenously and provide a strong platform to establish an independent scientific career.